It has been demonstrated in several trials that G-CSF and GM-CSF 
accelerate neutrophil recovery in patients following ABMT (16-21). 
The median number of days of absolute neutropenia (ANC < 500/jil) 
with ICE at the MTD in the Phase I ABMT study was 17 and we will 
attempt to shorten this with the addition of G-CSF. 
Mechanism of Marrow Reconstitution after High Dose Chemotherapy 
and ABMT 
It is not currently known whether it is feasible to achieve bone 
marrow engraftment after supra-lethal doses of chemotherapy with 
genetically-altered bone marrow stem cells. If such a goal was 
achievable, this approach would offer therapeutic potential for a 
number of diseases. Critical questions concerning the ability to 
transduce hematopoietic stem cells with marker genes and the 
ability to achieve long-term gene expression are discussed below. 
However, another important question is whether it is ever possible 
in the autologous bone marrow transplant setting to achieve long 
term marrow reconstitution from reinfused hematopoietic stem 
cells. In the murine system, a population of cells has been 
functionally identified by its capacity to provide short-term 
repopulation or radioprotection. Another population of cells 
provides long-term engraftment as assayed at 4-6 months (22, 23, 
39). The source of these long-term repopulating stem cells, whether 
reinfused or endogenous, is unknown. 
There are no methods currently available to definitively determine 
the source of the stem cells responsible for short or long-term 
marrow reconstitution after high dose chemotherapy. The use of 
retroviral vectors to transduce stem cells with the neo marker gene 
provides such an opportunity. We will transduce CD34+ enriched 
bone marrow stem cells and progenitor cells with a retroviral 
vector containing the bacterial neomycin resistance gene. These 
ceils will be reinfused into patients along with non-transduced bone 
marrow mononuclear cells following high dose ICE chemotherapy and 
their trafficking patterns in the peripheral blood and bone marrow 
studied by PCR analysis. We will transduce the subpopulation of 
CD34+ cells with the neo gene because the pluripotent stem cells 
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Recombinant DNA Research, Volume 16 
